Conventional dry cells are usually tubular in shape with a positive terminal on one end and a negative terminal on the other end. When the cells are used in a multicell device, such as flashlights, radios and tape recorders, they are commonly aligned in an end-to-end configuration so that the positive terminal of one battery contacts the negative terminal of a second adjacent battery. While directions on how to properly insert cells into a device are usually provided by the device manufacturer, a small percentage of battery users inadvertently insert at least one of the cells into the device so that the electrical polarities of the cell's terminals are incorrectly reversed. In a device that uses two or more cells aligned end-to-end, a cell has been inserted in reverse when one of the cell's terminals contacts an identical terminal on an adjacent cell and the abutting terminals have the same electrical polarity. The primary danger associated with a reversed cell is that the properly oriented cells may charge the reversed cell when the device is turned on. Charging a cell leads to an increase in internal pressure due to the generation of hydrogen gas and may lead to activation of the cell's safety vent. Leakage of electrolyte through the ruptured safety vent is the net result. In addition, incorrect orientation of a cell in a device, commonly known as cell reversal, should be avoided because of the electrical damage that can be done to the device's electrical components when the cell's electrical current is forced backwards through the device's electrical circuit.
Insuring correct electrical orientation of a cylindrical cell's electrical terminals when the cell is inserted into a device that uses two or more cells aligned end-to-end is a problem that has been addressed numerous times. An examination of the prior art reveals that some of the proposed solutions to the cell reversal problem depend upon the reversed cell's terminal directly contacting one of the device's terminals. For example, U.S. Pat. No. 4,595,641 describes a battery compartment that uses an insulating member on the device's positive contact assembly to prevent electrical contact with the negative terminal of an improperly inserted cell while an insulating member on the device's negative contact assembly is used to prevent electrical contact with the positive terminal of an improperly inserted cell.
Another concept utilizes modifications to the device's terminal so that a device can accomodate a cell regardless of how the cell is inserted. U.S. Pat. No. 4,622,274 describes a terminal construction for an electric power supply. The terminal design is independent of the battery's orientation. Therefore, the battery can be switched end-to-end without affecting the contact between the battery and the mating circuit in the receiving device.
U.S. Pat. No. 4,002,808 describes the use of a mechanical link, such as a spring-catch system, screwing or locking, to provide for reliable mechanical and electrical linkage between cylindrical electrical cells that are connected in an end-to-end configuration.
JP 61-22566, a Japanese Kokai patent, discloses a cylindrical alkaline battery whose positive and negative terminals are recessed below the crimped over portions of the outer metal jacket.
U.S. Pat. No. 4,869,978 describes the use of an electrically insulating film to prevent an electrical short circuit between the positive electrode case and the bottom plate. In another embodiment, an electrically insulating film is positioned between the negative electrode terminal and the washer or between the gasket and the washer in order to prevent the formation of a local cell which could result in the leakage of electrolytic solution.
Cylindrical alkaline batteries made with the plastic label extended over a portion of the negative terminal are available as a commercial product. The centrally located and electrically conductive portion of the negative cover is recessed slightly below the insulating label which protects the terminal's circular edge.
The known methods of preventing cell reversal have met with limited success. However, none of the solutions known in the art prior to the subject invention were able to prevent the flow of electric current between adjacent cells when the reversed cell was made with conventional terminals and positioned between two cells in a device that uses three or more cells aligned end-to-end.